An article appearing in the "ROBOTICS AGE" magazine, November/December 1982 issue entitled "Robot Wrist Actuators" pages 15-19 summarizes the state of development of wrist mechanisms for robots and other similar automatic machine tools. This article includes a bibliography listing of a number of prior art United States and foreign patents as well as published articles concerning wrist mechanisms. As noted in the first two paragraphs of this article, it is stated that the wrist actuator takes ninety percent of the creativity of the mechanical design of the industrial robot. It is further stated that the ideal wrist is one which is compact, powerful, dexterous and precise. It is further stated that most robots used in welding, material handling, paint spraying, assembly, and working in cramped spaces or performing complex maneuvers would benefit from improved wrist design.
The article further describes a number of known wrist designs and in particular the wrist mechanism employed on the Cincinnatti Milacron-Roll wrist as described on page 10 of the article. The wrist design there disclosed is quite complex, heavy and expensive. This is due to the fact that for manipulator work, one of the big requirements is load capacity and because of that the wrist is made quite large and heavy. It is also designed to provide for three dimensional articulation and hence complex. However, many applications for wrist mechanisms do not need the kind of capacity and dexterity that is built into the design of the three dimensional prior art wrist actuators such as are described in the above-noted article. For example, gas torch cutting, spray painting, welding, brazing, dispensing on mastic material and perhaps even space robot work do not require large load handling capability and could instead use a manipulator that is light weight, simple in design and relatively low cost but sufficiently dexterous and precise for many job applications. Such a manipulator also could be used in machine shops employing NC machines which are capable of moving a tool holding member selectively along one axis of movement, two orthogonal axes of movement within a plane, or three orthogonally arrayed axes of movement for three dimensional positioning. There is a further possibility of need in the medical field for positioning x-ray guns and the like where a simple, light weight, less expensive wrist mechanism can do the job satisfactorily without requiring the large load carrying capability or additional degrees of movement designed into the existing wrist actuators as depicted in the above-noted article.